Integrated process for the treatment of a methane-containing wet gas in order to remove water therefrom

Abstract

A gas containing methane and water is treated in order to remove water therefrom. The process comprises a step of contacting the gas with a liquid phase formed of water and solvent, whereby water free of solvent can be removed, and a subsequent step of cooling the resultant gas. The process is applicable to natural gas and to refinery gas.

What is claimed as the invention is: 
     
       1. A process for the treatment of a methane and water-containing gas in order to remove at least a part of said water from the gas, comprising the steps of: (a) contacting said gas with a recycled liquid phase containing both water and introduced solvent, said solvent being a non-hydrocarbon compound other than water and being miscible with water, maintaining contact conditions adapted to vaporize and transfer to the gas at least 90% of the introduced solvent amount originating from the recycled liquid phase, discharging the liquid aqueous phase resulting from said contact and containing less than 10% of the introduced solvent amount, and recovering a gas containing in a vaporized state at least 90% of the introduced solvent amount;   (b) cooling the gas obtained in step (a), to condense a liquid fraction essentially formed of solvent and water;   (c) separating residual uncondensed gas from said liquid fraction and recycling to step (a) resultant separated liquid fraction containing solvent and water, to form the recycled liquid phase.   
     
     
       2. A process according to claim 1, wherein the molar ratio of the solvent flow rate to the flow rate of treated gas during step (a) ranges from 1/1000 to 1/10. 
     
     
       3. A process according to claim 1, wherein the solvent is an alcohol. 
     
     
       4. A process according to claim 1, wherein the solvent is methanol. 
     
     
       5. A process according to claim 1, wherein the solvent is a solvent forming an azeotrope with water. 
     
     
       6. A process according to claim 1, wherein the solvent is ethanol, 2-methoxyethanol, propanol, butanol, propargyl alcohol, pyridine, or piperidine. 
     
     
       7. A process according to claim 1 wherein step (a) is conducted in a vertical column and the contact is counter-current between rising gas and descending recycled liquid phase. 
     
     
       8. A process according to claim 1, wherein before cooling in step (b), a gas fraction originating from subsequent step (g) is added to the gas obtained in step (a), and: (d) the residual gas originating from the separation step (c) is admixed with a fraction containing solvent in liquid phase originating from step (g);   (e) the liquid-gas mixture originating from step (d) is cooled so as to produce a liquid fraction essentially formed of solvent and water and a gas fraction;   (f) the obtained fractions are separated after the cooling step (e), and   (g) a part of the gas fraction separated in step (f) is discharged as purified gas and another part of said gas fraction separated in step (f) is contacted with at least a portion of the solvent and water liquid fraction separated in step (f), at a temperature higher than that of step (f), thus producing a liquid fraction essentially formed of solvent and a gas fraction, and recycling said liquid fraction to step (d) and adding said gas fraction to the gas obtained in step (a).   
     
     
       9. A process according to claim 1, applied to a gas further containing at least one hydrocarbon other than methane, condensable in the conditions of step (b) by forming a hydrocarbon liquid fraction separate from said fraction consisting essentially of solvent and water, and said hydrocarbon liquid fraction is separated and discharged from the process. 
     
     
       10. A process according to claim 9, wherein the hydrocarbon liquid fraction formed during step (b) is contacted with water so as to transfer to water at least a part of the solvent dissolved in the hydrocarbon liquid fraction, so as to obtain a hydrocarbon liquid phase at least partially free of solvent and a water and solvent liquid phase which may be admixed to the liquid phase recycled from step (c) to step (a). 
     
     
       11. A process according to claim 1, wherein the treated gas is subjected to an additional treatment step for removing at least a portion of acid gases present in said gas, the treated gas being contacted with solvent in sufficient amount to dissolve the acid gases to be removed and the solvent phase obtained from this contact operation being expanded so as to produce at least one gas fraction which is removed and a liquid phase which is recycled to said additional treatment. 
     
     
       12. A process according to claim 10, wherein gas fraction obtained after expansion of the solvent is contacted with water so as to transfer to water at least a portion of the solvent contained in said gas fraction, the obtained water and solvent solution being admixed with the liquid phase recycled from step (c) to step (a). 
     
     
       13. A process according to claim 1, wherein the solvent is added to the gas obtained in step (a), before proceeding to step (b), in sufficient amount to compensate for the losses and to maintain a stable operation. 
     
     
       14. A process according to claim 1, wherein the contact conditions are so selected as to maintain a solvent concentration from 0.01 to 5% by weight in the aqueous liquid phase discharged from step (a). 
     
     
       15. A process according to claim 1, wherein the gas to be treated is divided into two parts before step (a), only a fraction of the total amount of the gas to be treated is contacted with the recycled liquid phase, the other gas fraction being admixed with the gas recovered after contact with the recycled liquid phase. 
     
     
       16. A process according to claim 13, wherein the portion of treated gas contacted with the recycled liquid phase amounts to 15-50% of the total amount of gas to be treated. 
     
     
       17. A process according to claim 1, wherein the required cooling of step (b) is obtained at least partly by expanding at least a portion of the treated gas through an expansion turbine and/or an expansion valve.